Mechanistic aspects of general acid catalysis of carbinolamine formation from substituted hydrazine derivatives and aromatic carbonyl compounds will be investigated by kinetic studies in aqueous solution. (a) The pH-rate profile and the Bronsted plot for general acid catalysis of the reaction of acethydrazide, CH3C(O)NHNH2, with p-chlorobenzaldehyde will be examined to determine whether this reaction proceeds by a preasssociation mechanism involving initial formation of a termolecular encounter complex of amine, aldehyde and acid, followed by rapid, reversible formation of a zwitterionic addition intermediate from the aldehyde and the amine, and protonation of this intermediate by the acid catalyst within the encounter complex in a subsequent step. (b) The effect of varying the basicity of the nitrogen nucleophile on the Bronsted alpha-values for general acid catalysis of carbinolamine formation from substituted hydrazines and p,p'-dihydroxybenzophenone will be determined. The information obtained from this correlation of alpha with the basicity of the nucleophile will be interpreted in terms of the shape of the three dimensional free energy-reaction coordinate diagrams for the reaction and the extent to which the proton transfer process in this acid catalyzed reaction may be "concerted" or coupled with carbon-nitrogen bond formation. These investigations are intended to provide fundamental information about mechanisms of general acid catalysis that should be applicable to the study of catalysis by enzymes, particularly the serine proteinases.